Lyng is a very simple language, where we take only most important and popular features from other scripts and languages. In particular, we adopt principle of minimal confusion[^1]. In other word, the code usually works as expected when you see it. So, nothing unusual.

Other documents to read maybe after this one:

Advanced topics
OOP notes
math in Lyng
Some class references: List, Real, Range, Iterable, Iterator
Some samples: combinatorics See samples folder

Expressions

Everything is an expression in Lyng. Even an empty block:

// empty block
>>> void

any block also returns it's last expression:

if( true ) {
    2 + 2
    3 + 3
}
>>> 6

If you don't want block to return anything, use void:

fn voidFunction() {
    3 + 4 // this will be ignored
    void
}
voidFunction()
>>> void

otherwise, last expression will be returned:

fn normalize(value, minValue, maxValue) {
    (value - minValue) / (maxValue-minValue)
}
normalize( 4, 0.0, 10.0)
>>> 0.4

Every construction is an expression that returns something (or void):

val x = 111 // or autotest will fail!
val limited = if( x > 100 ) 100 else x
limited
>>> 100

You can use blocks in if statement, as expected:

val x = 200
val limited = if( x > 100 ) {
    100 + x * 0.1    
}
else 
    x
limited
>>> 120.0

When putting multiple statments in the same line it is convenient and recommended to use ;:

var from; var to
from = 0; to = 100
>>> 100

Notice: returned value is 100 as assignment operator returns its assigned value. Most often you can omit ;, but improves readability and prevent some hardly seen bugs.

Assignments

Assignemnt is an expression that changes its lvalue and return assigned value:

var x = 100
x = 20
println(5 + (x=6)) // 11: x changes its value!
x
>>> 11
>>> 6

As the assignment itself is an expression, you can use it in strange ways. Just remember to use parentheses as assignment operation insofar is left-associated and will not allow chained assignments (we might fix it later). Use parentheses insofar:

var x = 0
var y = 0
x = (y = 5)
assert(x==5)
assert(y==5)
>>> void

Note that assignment operator returns rvalue, it can't be assigned.

Modifying arithmetics

There is a set of assigning operations: +=, -=, *=, /= and even %=.

var x = 5
assert( 25 == (x*=5) )
assert( 25 == x)
assert( 24 == (x-=1) )
assert( 12 == (x/=2) )
x
>>> 12

Notice the parentheses here: the assignment has low priority!

These operators return rvalue, unmodifiable.

Assignment return r-value!

Math

It is rather simple, like everywhere else:

val x = 2.0
sin(x * π/4) / 2.0
>>> 0.5

See math for more on it. Notice using Greek as identifier, all languages are allowed.

Logical operation could be used the same

var x = 10
++x >= 11
>>> true

Supported operators

op	ass	args	comments
+	+=	Int or Real
-	-=	Int or Real	infix
*	*=	Int or Real
/	/=	Int or Real
%	%=	Int or Real
&&		Bool
\|\|		Bool
!x		Bool
<		String, Int, Real	(1)
<=		String, Int, Real	(1)
>=		String, Int, Real	(1)
>		String, Int, Real	(1)
==		Any	(1)
===		Any	(2)
!==		Any	(2)
!=		Any	(1)
++a, a++		Int
--a, a--		Int

(1): comparison are based on comparison operator which can be overloaded
(2): referential equality means left and right operands references exactly same instance of some object. Note that all singleton object, like null, are referentially equal too, while string different literals even being equal are most likely referentially not equal

Reference quality and object equality example:

assert( null == null)  // singletons
assert( null === null)
// but, for non-singletons:
assert( 5 == 5)
assert( 5 !== 5)
assert( "foo" !== "foo" )
>>> void

Variables

Much like in kotlin, there are variables:

var name = "Sergey"

Variables can be not initialized at declaration, in which case they must be assigned before use, or an exception will be thrown:

var foo
// WRONG! Exception will be thrown at next line:
foo + "bar"

Correct pattern is:

foo = "foo"
// now is OK:
foo + bar

This is though a rare case when you need uninitialized variables, most often you can use conditional operators and even loops to assign results (see below).

Constants

Almost the same, using val:

val foo = 1
foo += 1 // this will throw exception

Constants

Same as in kotlin:

val HalfPi = π / 2

Note using greek characters in identifiers! All letters allowed, but remember who might try to read your script, most likely will know some English, the rest is the pure uncertainty.

Defining functions

fun check(amount) {
    if( amount > 100 )
        "enough"
    else
        "more"
}
>>> Callable@...

Notice how function definition return a value, instance of Callable.

You can use both fn and fun. Note that function declaration is an expression returning callable, but Lyng syntax requires using the lambda syntax to create such.

val check = { 
    it > 0 && it < 100
}
assert( check(1) )
assert( !check(101) )
>>> void

See lambdas section below.

There are default parameters in Lyng:

fn check(amount, prefix = "answer: ") {
    prefix + if( amount > 100 )
        "enough"
    else
        "more" 
}
assert( "do: more" == check(10, "do: ") )
check(120)
>>> "answer: enough"

Closures

Each block has an isolated context that can be accessed from closures. For example:

var counter = 1

// this is ok: counter is incremented
fun increment(amount=1) {
    // use counter from a closure:
    counter = counter + amount
}

increment(10)
assert( counter == 11 )

val callable = {
    // this obscures global outer var with a local one
    var counter = 0
    // ...
    counter = 1
    // ...
    counter
}

assert(callable() == 1)
// but the global counter is not changed:
assert(counter == 11)
>>> void

Lambda functions

Lambda expression is a block with optional argument list ending with ->. If argument list is omitted, the call arguments will be assigned to it:

lambda = {
    it + "!"
}
assert( lambda is Callable)
assert( lambda("hello") == "hello!" )
void

`it` assignment rules

When lambda is called with:

no arguments: it == void
exactly one argument: it will be assigned to it
more than 1 argument: it will be a List with these arguments:

Here is an example:

val lambda = { it }
assert( lambda() == void )
assert( lambda("one") == "one")
assert( lambda("one", "two") == ["one", "two"])
>>> void

If you need to create unnamed function, use alternative syntax (TBD, like { -> } ?)

Declaring parameters

Parameter is a list of comma-separated names, with optional default value; last one could be with ellipsis that means "the rest pf arguments as List":

assert( { a -> a }(10) == 10 )
assert( { a, b -> [a,b] }(1,2) == [1,2])
assert( { a, b=-1 -> [a,b] }(1) == [1,-1])
assert( { a, b...-> [a,...b] }(100) == [100]) 
// notice that splat syntax in array literal unrills
// ellipsis-caught arguments back:
assert( { a, b...-> [a,...b] }(100, 1, 2, 3) == [100, 1, 2, 3]) 
void

Using lambda as the parameter

// note that fun returns its last calculated value,
// in our case, result after in-place addition:
fun mapValues(iterable, transform) {
    var result = []
    for( x in iterable ) result += transform(x)
}
assert( [11, 21, 31] == mapValues( [1,2,3], { it*10+1 }))
>>> void

Auto last parameter

When the function call is follower by the { in the same line, e.g. lambda immediately after function call, it is treated as a last argument to the call, e.g.:

fun mapValues(iterable, transform) {
    var result = []
    for( x in iterable ) result += transform(x)
}
val mapped = mapValues( [1,2,3]) { 
    it*10+1 
}
assert( [11, 21, 31] == mapped)
>>> void

Lists (aka arrays)

Lyng has built-in mutable array class List with simple literals:

[1, "two", 3.33].size
>>> 3

List is an implementation of the type Array, and through it Collection and Iterable.

Lists can contain any type of objects, lists too:

val list = [1, [2, 3], 4]
assert( list is List )      // concrete implementatino
assert( list is Array )     // general interface
assert(list.size == 3)
// second element is a list too:
assert(list[1].size == 2)
>>> void

Notice usage of indexing. You can use negative indexes to offset from the end of the list; see more in Lists.

When you want to "flatten" it to single array, you can use splat syntax:

[1, ...[2,3], 4]
>>> [1, 2, 3, 4]

Of course, you can splat from anything that is List (or list-like, but it will be defined later):

val a = ["one", "two"]
val b = [10.1, 20.2]
["start", ...b, ...a, "end"]
>>> ["start", 10.1, 20.2, "one", "two", "end"]

Of course, you can set any list element:

val a = [1, 2, 3]
a[1] = 200
a
>>> [1, 200, 3]

Lists are comparable, and it works well as long as their respective elements are:

assert( [1,2,3] == [1,2,3])

// but they are _different_ objects:
assert( [1,2,3] !== [1,2,3])

// when sizes are different, but common part is equal,
// longer is greater
assert( [1,2,3] > [1,2] )

// otherwise, where the common part is greater, the list is greater:
assert( [1,2,3] < [1,3] )
>>> void

The simplest way to concatenate lists is using + and +=:

// + works to concatenate iterables: 
assert( [5, 4] + ["foo", 2] == [5, 4, "foo", 2])
var list = [1, 2]

// append allow adding iterables: all elements of it:
list += [2, 1]      
// or you can append a single element:
list += "end"
assert( list == [1, 2, 2, 1, "end"])
>>> void

Important note: the pitfall of using += is that you can't append in Iterable instance as an object: it will always add all its contents. Use list.add to add a single iterable instance:

var list = [1, 2]
val other = [3, 4]

// appending lists is clear:
list += other
assert( list == [1, 2, 3, 4] )

// but appending other Iterables could be confusing:
list += (10..12)
assert( list == [1, 2, 3, 4, 10, 11, 12])
>>> void

Use list.add to avoid confusion:

var list = [1, 2]
val other = [3, 4]

// appending lists is clear:
list.add(other)
assert( list == [1, 2, [3, 4]] )

// but appending other Iterables could be confusing:
list.add(10..12)
assert( list == [1, 2, [3, 4], (10..12)])
>>> void

To add elements to the list:

val x = [1,2]
x.add(3)
assert( x == [1,2,3])
// same as x += ["the", "end"] but faster:
x.add("the", "end")
assert( x == [1, 2, 3, "the", "end"])
>>> void

Self-modifying concatenation by += also works:

val x = [1, 2]
x += [3, 4]
assert( x == [1, 2, 3, 4])
>>> void

You can insert elements at any position using addAt:

val x = [1,2,3]
x.addAt(1, "foo", "bar")
assert( x == [1, "foo", "bar", 2, 3])
>>> void

Using splat arguments can simplify inserting list in list:

val x = [1, 2, 3]
x.addAt( 1, ...[0,100,0])
x
>>> [1, 0, 100, 0, 2, 3]

Using negative indexes can insert elements as offset from the end, for example:

val x = [1,2,3]
x.addAt(-1, 10)
x
>>> [1, 2, 10, 3]

Note that to add to the end you still need to use add or positive index of the after-last element:

val x = [1,2,3]
x.addAt(3, 10)
x
>>> [1, 2, 3, 10]

Removing list items

val x = [1, 2, 3, 4, 5]
x.removeAt(2)
assert( x == [1, 2, 4, 5])
// or remove range (start inclusive, end exclusive):
x.removeRangeInclusive(1,2)    
assert( x == [1, 5])
>>> void

Again, you can use negative indexes. For example, removing last elements like:

val x = [1, 2, 3, 4, 5]

// remove last:
x.removeAt(-1)
assert( x == [1, 2, 3, 4])

// remove 2 last:
x.removeRangeInclusive(-2,-1)
assert( x == [1, 2])
>>> void

Flow control operators

if-then-else

As everywhere else, and as expression:

val count = 11
if( count > 10 )
    println("too much")
else {
    // do something else
    println("just "+count)
}
>>> too much
>>> void

Notice returned value void: it is because of println have no return value, e.g., void.

Or, more neat:

var count = 3
println( if( count > 10 ) "too much" else "just " + count )
>>> just 3
>>> void

while

Regular pre-condition while loop, as expression, loop returns it's last line result:

var count = 0
while( count < 5 ) {
    count++
    count * 10
}
>>> 50

We can break as usual:

var count = 0
while( count < 5 ) {
    if( count < 5 ) break
    count = ++count * 10
}
>>> void

Why void? Because break drops out without the chute, not providing anything to return. Indeed, we should provide exit value in the case:

var count = 0
while( count < 50 ) {
    if( count > 3 ) break "too much"
    count = ++count * 10
    "wrong "+count
}
>>> "too much"

Breaking nested loops

If you have several loops and want to exit not the inner one, use labels:

var count = 0
// notice the label:
outerLoop@ while( count < 5 ) {
    var innerCount = 0
    while( innerCount < 100 ) {
        innerCount = innerCount + 1

        if( innerCount == 5 && count == 2 )
            // and here we break the labelled loop:
            break@outerLoop "5/2 situation"
    }
    count = count + 1
    count * 10
}
>>> "5/2 situation"

and continue

We can skip the rest of the loop and restart it, as usual, with continue operator.

var count = 0
var countEven = 0
while( count < 10 ) {
    count = count + 1
    if( count % 2 == 1) continue
    countEven = countEven + 1
}
"found even numbers: " + countEven
>>> "found even numbers: 5"

continue can't "return" anything: it just restarts the loop. It can use labeled loops to restart outer ones (we intentionally avoid using for loops here):

var count = 0
var total = 0
// notice the label:
outerLoop@ while( count++ < 5 ) {
    var innerCount = 0
    while( innerCount < 10 ) {
        if( ++innerCount == 10 )
            continue@outerLoop
    }
    // we don't reach it because continue above restarts our loop
    total = total + 1
}
total
>>> 0

Notice that total remains 0 as the end of the outerLoop@ is not reachable: continue is always called and always make Lyng to skip it.

else statement

The while and for loops can be followed by the else block, which is executed when the loop ends normally, without breaks. It allows override loop result value, for example, to not calculate it in every iteration. For example, consider this naive prime number test function (remember function return it's last expression result):

fun naive_is_prime(candidate) {
    val x = if( candidate !is Int) candidate.toInt() else candidate
    var divisor = 1
    while( ++divisor < x/2 || divisor == 2 ) {
        if( x % divisor == 0 ) break false
    }
    else true
}
assert( !naive_is_prime(16) )
assert( naive_is_prime(17) )
assert( naive_is_prime(3) )
assert( !naive_is_prime(4) )
>>> void

Loop return value diagram

flowchart TD
    S((start)) --> Cond{check}
    Cond--false, no else--->V((void))
    Cond--true-->E(["last = loop_body()" ])
    E--break value---->BV((value))
    E--> Check2{check}
    E--break---->V
    Check2 --false-->E
    Check2 --true, no else--->L((last))
    Check2 --true, else-->Else(["else_clause()"])
    Cond--false, else--->Else
    Else --> Ele4$nr((else))

So the returned value, as seen from diagram could be one of:

void, if the loop was not executed, e.g. condition was initially false, and there was no else clause, or if the empty break was executed.
value returned from `break value' statement
value returned from the else clause, of the loop was not broken
value returned from the last execution of loop body, if there was no break and no else clause.

For loops

For loop are intended to traverse collections, and all other objects that supports size and index access, like lists:

var letters = 0
for( w in ["hello", "wolrd"]) {
    letters += w.length
}
"total letters: "+letters
>>> "total letters: 10"

For loop support breaks the same as while loops above:

fun search(haystack, needle) {    
    for(ch in haystack) {
        if( ch == needle) 
            break "found"
    }
    else null
}
assert( search("hello", 'l') == "found")
assert( search("hello", 'z') == null)
>>> void

We can use labels too:

fun search(haystacks, needle) {    
    exit@ for( hs in haystacks ) {
            for(ch in hs ) {
                if( ch == needle) 
                    break@exit "found"
            }
        }
        else null
}
assert( search(["hello", "world"], 'l') == "found")
assert( search(["hello", "world"], 'z') == null)
>>> void

Self-assignments in expression

There are auto-increments and auto-decrements:

var counter = 0
assert(counter++ * 100 == 0)
assert(counter == 1)
>>> void

but:

var counter = 0
assert( ++counter * 100 == 100)
assert(counter == 1)
>>> void

The same with --:

var count = 100
var sum = 0
while( count > 0 ) sum = sum + count--
sum
>>> 5050

There are self-assigning version for operators too:

var count = 100
var sum = 0
while( count > 0 ) sum += count--
sum
>>> 5050

Ranges

Ranges are convenient to represent the interval between two values:

5 in (0..100)
>>> true

It could be open and closed:

assert( 5 in (1..5) )
assert( 5 !in (1..<5) )
>>> void

Ranges could be inside other ranges:

assert( (2..3) in (1..10) )
>>> void

There are character ranges too:

'd' in 'a'..'e'
>>> true

and you can use ranges in for-loops:

for( x in 'a' ..< 'c' ) println(x)
>>> a
>>> b
>>> void

See Ranges for detailed documentation on it.

Comments

// single line comment
var result = null // here we will store the result
>>> void

Integral data types

type	description	literal samples
Int	64 bit signed	`1` `-22` `0x1FF`
Real	64 bit double	`1.0`, `2e-11`
Bool	boolean	`true` `false`
Char	single unicode character	`'S'`, `'\n'`
String	unicode string, no limits	"hello" (see below)
List	mutable list	[1, "two", 3]
Void	no value could exist, singleton	void
Null	missing value, singleton	null
Fn	callable type

Character details

The type for the character objects is Char.

Char literal escapes

Are the same as in string literals with little difference:

escape	ASCII value
\n	0x10, newline
\t	0x07, tabulation
\	\ slash character
'	' apostrophe

Char instance members

assert( 'a'.code == 0x61 ) 
>>> void

member	type	meaning
code	Int	Unicode code for the character

String details

String operations

Concatenation is a +: "hello " + name works as expected. No confusion.

Literals

String literal could be multiline:

"Hello
World"

though multiline literals is yet work in progress.

Built-in functions

See math functions. Other general purpose functions are:

name	description
assert(condition,message="assertion failed")	runtime code check. There will be an option to skip them
println(args...)	Open for overriding, it prints to stdout.

Built-in constants

name	description
Real, Int, List, String, List, Bool	Class types for real numbers
π	See math

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Lyng tutorial

Expressions

Assignments

Modifying arithmetics

Assignment return r-value!

Math

Supported operators

Variables

Constants

Constants

Defining functions

Closures

Lambda functions

it assignment rules

Declaring parameters

Using lambda as the parameter

Auto last parameter

Lists (aka arrays)

Removing list items

Flow control operators

if-then-else

while

Breaking nested loops

and continue

else statement

Loop return value diagram

For loops

Self-assignments in expression

Ranges

Comments

Integral data types

Character details

Char literal escapes

Char instance members

String details

String operations

Literals

Built-in functions

Built-in constants

22 KiB

Raw Blame History

`it` assignment rules